If you receive this error when trying to upload an attachment, it means that you have passed the extension file validation in the system property: glide.attachment.extensions but you are not passing the MIME validation (an extra security validation).
To solve that issue, you need to add this file type to "glide.security.mime_type.aliasset" property.
You must check the error in the logs (you can filter by warning and message contains "mime" word). There you will see something like this:
MIME type mismatch for file: xxxx.xlsm . Expected type: application/vnd.ms-excel.sheet.macroenabled.12, Actual type: application/x-tika-ole-drm-encrypted"
You just need to add in "glide.security.mime_type.aliasset" the following value using type String:
application/x-tika-ole-drm-encrypted=application/vnd.ms-excel.sheet.macroenabled.12
This is an example, you can add more file types as you need cheking the logs and using comma.
Here some information about tika, it can be helpful:
https://tika.apache.org/2.4.1/formats.html
